Endianity with Linux on Itanium hardware

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emilsa · Post by **emilsa** » Sun May 22, 2005 4:26 pm

I've been asked to install Linux on HP-Itanium Hardware. Major demand of this installation is full big endian support.
As far as I know, all Linux distros for Itanium hardware precompiled with little endian support, nevertheless that Itanium processor support big endian. As well PPC version of Linux is big endian.

My question is: is it possible (even theoretically) to compile Linux to be big endian on Itanium ?

yaneurabeya · Post by **yaneurabeya** » Sun May 22, 2005 8:07 pm

I thought all Intel hardware ran big endian based number crunching, etc. However, I could be wrong...

Redhatter · Post by **Redhatter** » Sun May 22, 2005 11:38 pm

Actually no... Intel IA32 (x86) is little endian... as is AMD64.

I've had a look around... everything I've found regarding IA64 mentions it being little endian... I'm doubtful as to whether IA64 can even run Big Endian.

Some arches can run both ways... MIPS is one... on SGI machines, the CPUs are generally configured big endian, and on Cobalt servers, little endian. In this case though, you need a different userland and compiller...

You'll notice that Cobalt servers use "mipsel-unknown-linux-gnu" as a CHOST, vs "mips-unknown-linux-gnu" on SGI machines... Guess what the "el" stands for...

I think you'd find, if it were possible, it would be a similar situation with IA64... although I'm no expert in the area, having never used it.

emilsa · Post by **emilsa** » Mon May 23, 2005 7:09 am

Actually all world running big endian. Only Intel uses little endian.
Itanium for sure running both: HP-UX on Itanium servers run big endian and Linux - little endian. CPU endianity controlled by boot loader.

My question is if it is possible to compile Linux for Itanium as big endian system ?

Redhatter · Post by **Redhatter** » Mon May 23, 2005 1:49 pm

Ahh okay, so the bootloader is able to switch the CPU into either mode. Therefore, yes, it definately should be possible, given an appropriate kernel and userland. (or cross-compiler to generate the said kernel and userland).

And to clarify... there's many more architectures than just Intel that use Little Endian. MIPS can be either (as I said before)... I'm pretty sure AMD64 is little-endian too... and I'm not sure about other architectures. I know for a definite fact, that PowerPC and Sparc are definately big endian.